Defer the real work in updateCompositingLayers until it's really needed.

Source/web/tests/ScrollingCoordinatorChromiumTest.cpp

Index: Source/web/tests/ScrollingCoordinatorChromiumTest.cpp
diff --git a/Source/web/tests/ScrollingCoordinatorChromiumTest.cpp b/Source/web/tests/ScrollingCoordinatorChromiumTest.cpp
index 9c6e80cd5f14398e223bd983fff891c3d980b8d7..d9713560bb41843347d3f335b10ca7babe1a0547 100644
--- a/Source/web/tests/ScrollingCoordinatorChromiumTest.cpp
+++ b/Source/web/tests/ScrollingCoordinatorChromiumTest.cpp
@@ -103,6 +103,12 @@ public:
         Platform::current()->unitTestSupport()->serveAsynchronousMockedRequests();
     }
 
+    void forceFullCompositingUpdate()
+    {
+        RenderLayerCompositor* compositor = m_webViewImpl->mainFrameImpl()->frame()->contentRenderer()->compositor();
+        compositor->updateCompositingLayers(CompositingUpdateFinishAllDeferredWork);
+    }
+
     void registerMockedHttpURLLoad(const std::string& fileName)
     {
         URLTestHelpers::registerMockedURLFromBaseURL(WebString::fromUTF8(m_baseURL.c_str()), WebString::fromUTF8(fileName.c_str()));
@@ -129,6 +135,7 @@ protected:
 TEST_F(ScrollingCoordinatorChromiumTest, fastScrollingByDefault)
 {
     navigateTo("about:blank");
+    forceFullCompositingUpdate();
 
     // Make sure the scrolling coordinator is active.
     FrameView* frameView = m_webViewImpl->mainFrameImpl()->frameView();
@@ -166,6 +173,7 @@ TEST_F(ScrollingCoordinatorChromiumTest, fastScrollingForFixedPosition)
 {
     registerMockedHttpURLLoad("fixed-position.html");
     navigateTo(m_baseURL + "fixed-position.html");
+    forceFullCompositingUpdate();
 
     // Fixed position should not fall back to main thread scrolling.
     WebLayer* rootScrollLayer = getRootScrollLayer();
@@ -250,6 +258,7 @@ TEST_F(ScrollingCoordinatorChromiumTest, nonFastScrollableRegion)
 {
     registerMockedHttpURLLoad("non-fast-scrollable.html");
     navigateTo(m_baseURL + "non-fast-scrollable.html");
+    forceFullCompositingUpdate();
 
     WebLayer* rootScrollLayer = getRootScrollLayer();
     WebVector<WebRect> nonFastScrollableRegion = rootScrollLayer->nonFastScrollableRegion();
@@ -262,6 +271,7 @@ TEST_F(ScrollingCoordinatorChromiumTest, wheelEventHandler)
 {
     registerMockedHttpURLLoad("wheel-event-handler.html");
     navigateTo(m_baseURL + "wheel-event-handler.html");
+    forceFullCompositingUpdate();
 
     WebLayer* rootScrollLayer = getRootScrollLayer();
     ASSERT_TRUE(rootScrollLayer->haveWheelEventHandlers());
@@ -271,6 +281,7 @@ TEST_F(ScrollingCoordinatorChromiumTest, clippedBodyTest)
 {
     registerMockedHttpURLLoad("clipped-body.html");
     navigateTo(m_baseURL + "clipped-body.html");
+    forceFullCompositingUpdate();
 
     WebLayer* rootScrollLayer = getRootScrollLayer();
     ASSERT_EQ(0u, rootScrollLayer->nonFastScrollableRegion().size());
@@ -280,6 +291,7 @@ TEST_F(ScrollingCoordinatorChromiumTest, overflowScrolling)
 {
     registerMockedHttpURLLoad("overflow-scrolling.html");
     navigateTo(m_baseURL + "overflow-scrolling.html");
+    forceFullCompositingUpdate();
 
     // Verify the properties of the accelerated scrolling element starting from the RenderObject
     // all the way to the WebLayer.
@@ -318,6 +330,7 @@ TEST_F(ScrollingCoordinatorChromiumTest, iframeScrolling)
     registerMockedHttpURLLoad("iframe-scrolling.html");
     registerMockedHttpURLLoad("iframe-scrolling-inner.html");
     navigateTo(m_baseURL + "iframe-scrolling.html");
+    forceFullCompositingUpdate();
 
     // Verify the properties of the accelerated scrolling element starting from the RenderObject
     // all the way to the WebLayer.
@@ -361,6 +374,7 @@ TEST_F(ScrollingCoordinatorChromiumTest, rtlIframe)
     registerMockedHttpURLLoad("rtl-iframe.html");
     registerMockedHttpURLLoad("rtl-iframe-inner.html");
     navigateTo(m_baseURL + "rtl-iframe.html");
+    forceFullCompositingUpdate();
 
     // Verify the properties of the accelerated scrolling element starting from the RenderObject
     // all the way to the WebLayer.
@@ -399,6 +413,7 @@ TEST_F(ScrollingCoordinatorChromiumTest, setupScrollbarLayerShouldNotCrash)
 {
     registerMockedHttpURLLoad("setup_scrollbar_layer_crash.html");
     navigateTo(m_baseURL + "setup_scrollbar_layer_crash.html");
+    forceFullCompositingUpdate();
     // This test document setup an iframe with scrollbars, then switch to
     // an empty document by javascript.
 }